Open Engineering
Environment and Development.

Saving Energy

Saving energy is cheaper than generating it: Negawatts cost less than Megawatts! In northern countries most energy used within houses is for space heating (61% in Britain), with heating hot water coming second. Hot countries don't have to spend on heating but can end up using just as much energy for cooling. Worse still while heating apparatus can be as simple as a wood burning stove, cooling requires expensive complex air-conditioning equipment that has to be imported. [Cambia a la versión en ESPANOL]

Yet it is possible to build houses in northern countries that require no additional heating: they are warmed by the sun, by body heat of the occupants and by heat released by lighting, cooking etc.; and they stay warm thanks to excellent insulation. Similarly houses can be built to stay cool in hot countries.

This page looks at ways to save energy:

Organising to Save Energy

While there are many things an individual can do to save energy, it is far more effective to involve a wider group. At work an Environmental Committee can be set up: it needs to have access to the management responsible for the workplace and also be able to convince people to participate individually, e.g. in switching off lights. Management often welcome environmental committees because apart environmental benefits they may also save them money.

In the UK there is an Eco Schools movement: schools take part by setting up an Eco Council involving pupils, teachers and parents, which then decides what measures the school will take.

Once you have set up an Environmental Committee, its first task is to find out how much energy is currently used and what it is used for. Once you know that, you can plan how to make savings. In some countries free assistance and advice is available for both these tasks (see the next section).

Getting Energy Saving Advice

Many countries now have organisations dedicated to offering energy advice, usually directly or indirectly funded by government. In the UK there are two large national organisations:

In addition local councils are offering energy advice, as are many independent organisations and charities, and the power companies (gas and electricity suppliers). Environmental organisations like Friends of the Earth and Greenpeace also do so.


Architects can save energy more cheaply than engineers can generate it! They can design buildings that require less energy to cool or heat, and they can use construction methods that require fewer energy inputs. A building that stays cool naturally goes on saving energy year after year for free, without expensive maintenance bills for air-conditioning.

(1) House in Nicaragua with thick walls, few windows, high ceiling and straw roof. (2) Narrow streets, white walls, and window shutters in Spain. (3) Cave house in Granada, Spain

Air Conditioning

How much energy do Air Conditioners use and what is the cost?

Ratings for air conditioning run by the number of British Thermal Units (BTU) an air conditioner can remove per hour. 12,000 BTU equals a ton. The Energy-Efficiency Rating (EER) is calculated by dividing the BTU per hour by the number of watts the air conditioner consumes. A higher number means better efficiency. All air conditioners being manufactured today must have an Energy Guide Label somewhere visible on the machine. An air conditioner with a higher EER may be more expensive but may save money in the long term as it consumes less electricity. Room air conditioning devices built after 1 January 1990 have been subject to national appliance standards of an 8.0 EER. The hotter the climate a home is in, the higher EER is recommended to be. Thus, homeowners living in homes in hot climates should seek to purchase an air conditioner with at least a 10.0 EER.

Typical air conditioners for the home are said to be in the 5,500 BTU to 14,000 BTU per hour range in the US, and in the UK one site advises a minimum BTU of 9000 to cool a small bedroom. I assume more powerful units are used in tropical countries: a domestic air conditioner might therefore use in the range of 800W to 2kW. The total energy used might therfore be:

For comparison, in my UK home I measured:

Large Fridge-Freezer (more modern units use half this):1.7 kWh per day
Electric Kettle (numerous cups of tea!):0.3 kWh per day
Electric Lights (all bulbs are low energy types):0.35 kWh per day
Total Electricity Consumption of house (N.B. heating, hot water and cooking use gas):4.8 kWh per day

Conclusion: Air conditioning uses a LOT of electricity! Let's consider how much it will cost to air condition one room of your home. Suppose a house has a 50 year life:

These are estimates could be improved upon my getting some data for typical houses, but they are enough to show that it is worth investing quite a lot of money to reduce or eliminate the need for air conditioning.

Now let's consider how this might affect national electricity consumption, using Nicaragua as an example. Annual Electricity consumption was 2.929 billion kWh in 2006. Population is 5.8m, so there are probably 1 million or more households. If 1 million houses used an air conditioner, annually they would use between:

It appears that domestic air conditioners alone could potentially increase the country's demand for electricity to several times what it is now. Greater use of air conditioners in offices, shops, hotels, etc. would push demand even higher.

Could Air Conditioners become much more efficient, as fridges have done? Fridges and Air Conditioners are similar in that you have a box and a heat pump that pumps heat out of the box at the same rate as it comes in through the walls. However, fridge manufacturers can reduce the amount of energy used by improving the insulation of the box, but air conditioner manufacturers cannot do that because the box is not made by them - it is the room you fit it in. Therefore low energy air conditioning is only possible in low energy buildings.

Naturally-Cooled Buildings

Modern naturally-cooled buildings don't seem to be very common - the normal practice for many offices and houses in hot countries often seems to be "build a solar oven and then fit air conditioning to it". Traditional houses in hot countries were usually adapted to the heat, as can be seen in some of the images on this page. Typically they have features like:

Narrow streets prevent the sun striking the walls of the houses, and shade pedestrians as well. Probably some of these techniques are not suitable or would require adaptation for countries where earthquakes occur.

In this section I have tried to supply some links to sources of information about naturally-cooled buildings, but I cannot verify the effectiveness of the construction techniques described. This is probably an area where some research and experimentation is required to find good designs that work well in local conditions.

(1) and (2) Passive cooling designs.

To get more information about Naturally-Cooled Buildings, search in English for terms like: natural cooling, passive solar, passive cooling, green building, eco house. The sites below has a lot of information and outline designs:

1) Arizona Solar Centre - Natural Cooling

"Passive cooling techniques can be used to reduce, and in some cases eliminate, mechanical air conditioning requirements in areas where cooling is a dominant problem. The cost and energy effectiveness of these options are both worth considering by homeowner and builders. Contained within this section are rules of thumb and an explanation or the essentials of passive cooling systems."

2) Build It Solar - Passive Cooling - A good list of links on passive and active cooling techniques.

Passive cooling systems take advantage of the thermal mass of the Earth. The outer few feet of the Earth heat up and cool off in response to surface weather. However, deeper in the earth, about four feet and beyond, the temperature is more constant (around 14 degrees C, 58 F). Here, the earth can be used to both cool and stabilize temperature if the home is appropriately designed. See: Earthship cooling. It would be interesting to check if this figure (14 C) is correct for the tropics?

There is a bibliography on passive solar cooling here:

Also interesting:

Some other links of possible interest to natural cooling are:

Low Energy, Green Buildings

Apart from heating and cooling there is interest in the whole environmental effect of buildings.

'Green Buildings' are buildings where all aspects of energy usage and environmental impact are considered. For example, substantial amounts of energy go into the construction of buildings, especially in firing bricks and making concrete. Architects have experimented with alternative materials that require less energy and may have other benefits such as low-cost or good thermal characteristics.

Water Consumption and Waste Water: The supply of piped water implies large expenditures of energy by the water company and water itself is a scarce resource in many countries. Buildings can capture rainwater for toilets, watering the garden, etc.

'Earthships' are cutting edge 'green' buildings, constructed using waste car tyres and other recycled materials. They use the planets natural systems to provide all utilities - using the sun's energy and rain to provide heat, power and water. They are buildings that heat and cool themselves, harvest their own water and use plants to treat their sewage. They are generally experimental buildings but demonstrate technologies that could be applied more widely. See: Earthship, Brighton, UK,, wikipedia: nave de tierra.

(1) Earthship in Brighton, UK. (2) Earthship cooling concept [Note: 58F = 14.4 Celsius].

The environmental centre CAT has an online catalogue with many books on 'Green Building'. Although these more often concern keeping warm rather that cool, several unusual construction techniques are described (Rammed Earth, Straw Bale, etc.) which may be of interest in developing cool buildings

Electrical Equipment

It is possible to save a great deal of electricity by using equipment differently and buying more eficient models. Heating or cooling uses a lot of energy, so any electrical appliance that gets hot in use, is likely to be consuming a lot. In cold countries, the heat produced by inefficient electric appliances at least helps to heat the house in the winter, but in a warm country this heat is useless, and worse still, if the house or office has an air conditioner, it will consume extra electricity to pump the heat outside.


Lighting: Replace old lightbulbs with modern LED lightbulbs which use 5 times less electricity. Take measures to avoid lights being left on unecessarily.

TVs, DVDs ... Anything with a Remote

TVs, Videos, DVDs, HiFis and other equipment that can go into standby (i.e. that you can turn on from a remote control): These all use electricity unless completely turned off (by a switch on the unit). While the amounts are small (4W to 10W) they add up and are continuous. Some units don't even have an OFF switch and have to be switched off at the wall socket or unplugged to stop them consuming electricity. If this is inconvenient, consider buying a switched multisocket extension cable.


Modern 'A' rated fridges use far less than older models (45% to 80% less).Frigorífico de bajo consumo energético, 45 - 80%. Ensure that air circulates easily to the cooling grill and dust it it occasionally. Adjust the thermostat if the fridge is colder than it needs to be.


Computers use a significant amount of electricity and are on for long periods. When buying, choose a low energy model; flat screens use less than CRTs and laptops use less than desktops. Set existing computers so that they go into standby (low power) after being left idle for a time or even eventually into hibernate (powered off but with state saved so that they start up where you left off). Switch them off at the end of the day. 'Standby' mode saves a lot of energy: a desktop and monitor that normally consume 120W may consume only 6W in standby. On Windows, the standby and hibernate controls are where you set screensavers; on Linux, try Preferences -> Power Management. Tufts Office of Sustainability. has a very full explanation of the energy savings possible by enabling a PC's standby or hibernate features - see the site map.


Airconditioning consumes a lot of electricity - a single air conditioner could use from 5 to 25 kWh per day! See Air Conditioning under the Architecture section.

Washing Machines and Dryers

Washing Machines now have environmental ratings for how much electricity and water they consume. Some machines heat their own water electrically but and others have connections for both hot and cold water, which may be better if you have a supply of hot water from a more environmentally friendly source such as a solar water heater. Hot air clothes dryers use a lot of electricity. Washing machines and dryers are not common items in developing countries but I read a case study of a hospital laundry in a hot African country that had washing machines and dryers supplied with electricity by diesel generators running on imported oil. Using solar heated water to supply the washing machines, and hanging out the laundry on a clothes line, would have saved a fortune.

Electric Kettles and Stoves

When boiling water (e.g. to make a cup of tea), put in only the water you need (but you must cover the heating element) - without measuring it's easy to put in 2 to 5 cups of water to make just one cup of coffee. Use lids on saucepans or a pressure cooker.

Possible energy savings are:

Four 60W bulbs on for 6 hours a day, replaced by compact fluorescents: (60-12)x6288 Wh per day
TV, DVDs, HiFi switch off for 20 hours a day instead of left in standby: (4+4+4)x20240 Wh per day
Old Fridge-Freezer replaced with modern efficient one: 45 - 80%800 Wh per day
Electric Kettle or Stove - measuring and boiling only the water you need.150 Wh per day
Total Electricity Saving: 1478 Wh or approx 1.5 kWh1.5 kWh per day
Total Cost Saving (@ $0.10 /kWh): 1.5 x 365 x 0.10 =$55 per year

Energy Saving Links